Mobile microwave oven

ABSTRACT

A mobile, low powered microwave oven is disclosed. The oven has top entry to the heating chamber, it is powered from the cigarette lighter, has the controls and display and the cooling vents also on the top surface of the oven. The oven is arranged to be secured to the seat by the seat belts in such a manner that the oven will operate while so secured. There is also a spill container in the heating chamber. Materials may be used that make the oven cabinet transparent.

RELATED APPLICATIONS

[0001] The present application claims priority from U.S. ProvisionalPatent Application, entitled Mobile Microwave Oven, Ser. No. 60/173,679,which application was filed on Dec. 29, 1999, by Peter S. Stutman, aU.S. citizen, of 27 Lillian Avenue, Sudbury, Mass., 01776 and whichprovisional is hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention generally relates to microwave ovens and morespecifically to microwave ovens for use in vehicles such as cars,trucks, and boats. It has features specific to operation from a standardDC power source found in such vehicles as well as features whichmechanically secure it within the vehicle.

BACKGROUND OF THE INVENTION

[0003] Microwave ovens designed for portable operation and operation invehicles have been proposed previously. U.S. Pat. No. 4,667,075 ofSakurai proposes using a three-phase AC alternator to supply power. U.S.Pat. No. 5,276,300 of Low et al, describes a microwave oven containingessentially an inverter to allow 12 volt DC operation. AGOR technologiesof Verson, France manufactures a similar product. These devices,operated at power levels of about 0.6-1.0 kW nominal require DC inputcurrents from a 12 volt source of approximately 100 amperes. This muchcurrent requires direct connection to the vehicle battery with veryheavy gauge wire or the dedicated alternator of Sakai and impliesmechanical and electrical installation skills beyond the range of theaverage consumer. The oven must also be somehow mounted to the vehicleso that it does not move around. The microwave ovens previouslydescribed are mechanically very similar. They feature a cavity with afront opening door; that is, with a vertical hinge. The timer andcontrol keypad is mounted vertically in proximity to the door and theyare very similar to or modifications of conventional consumer microwaveovens.

[0004] Conventional consumer microwave ovens have power ratings in the500W-1000W range. These ratings represent the power delivered into theoven cavity. The nameplate power consumption of these microwave ovens istypically 50-75% higher. For example a Magic Chef MC-03JS CompactMicrowave oven is rated at 500 Watts and is rated at a power consumptionof 750 Watts. While these ovens could be powered by a DC to AC inverterof appropriate output, the inverter would have to be hardwired withheavy gauge wire, such as No. 0, to the vehicle battery or alternator inorder to receive the necessary current. If we assume a 90% inverterefficiency the 500 Watts oven mentioned above would cause a typicalinverter to draw a current of about 60 amperes at a nominal 13.8 volts.

SUMMARY OF THE INVENTION

[0005] This invention is a small, low-power, approximately 200 Wattmagnetron-type microwave oven. The invention described herein isdesigned to be powered by a vehicle's “accessory power” or “cigarettelighter” jack and to be held in place on a seat by a standard vehicleseat-belt. Also described is an upward-opening door and plasticradio-transparent microwave cavity liner designed to contain spilledfoods and facilitate cleaning. Methods of retaining food containerswhich hold the foods being heated, as well as other safety andconvenience features useful for real-world operation in the mobileenvironment are described.

[0006] It is envisioned that the device described will find wideapplication in cars, trucks, recreational vehicles, boats and simpleliving situations which do not provide conventional AC mains and inwhich consumers are unlikely to perform or have performed involvedinstallations. It can be used for many tasks, from heating baby bottlesand meals in properly designed containers, to heating the morning'scoffee, to warming automotive gasket materials in cold climates duringrepair operations.

[0007] In the preferred embodiment, a high frequency switching powersupply generates the required filament and high voltage necessary formagnetron operation. This is more efficient than suffering DC/ACinverter losses in addition to the losses seen in the typical microwaveoven power transformer. The magnetron is the type whose magnetic fieldis generated by permanent magnets.

[0008] The only readily available electrical outlet or jack in mostmodem cars and trucks and smaller boats is the familiar “cigarettelighter” or “accessory power” socket. This socket is familiar tomillions of users who power mobile phones, radar detectors, smallinverters and other convenience devices from them. These jacks aretypically fused at 15-30 amperes. This limits total electrical powerinput to the microwave oven described here to a range of approximately200-400 Watts. This corresponds to a typical microwave power rating ofabout 125-250 Watts. Most users of microwave ovens are used to largerpower inputs as mentioned previously. Therefore the cooking time in thislow power microwave oven will be longer than the “standard” timesexperienced in larger, more powerful units. For example, if it takes 1minute to heat a cup of soup to serving temperature in a 750 Wattmicrowave oven found in a typical American kitchen, it will take threeminutes nominally in a 250 Watt unit. In fact, given the significantincrease in cooking times, there will be thermal losses includingradiational and convective losses which will tend to cool the food beingheated and which will lengthen the required time beyond the simple ratioof power. In one mode the invention described here takes the “standard”cooking time for a 750-900 Watt microwave oven and automaticallymultiplies it by an appropriate factor to arrive at the correct heatingtime for this lower-power oven. In another mode the user enters adesired heating interval which is not multiplied by any factor.

[0009] The invention described herein also senses input current andvoltage. It shuts down if excessive current is drawn to protect the“accessory socket’ fuse or if voltage drops to a level just above thatwhich corresponds to the vehicle battery being unable to start thevehicle.

[0010] A microwave oven, even a small one, is a substantial mass, and itmay contain foods which are near or at the boiling point. It must besecurely mounted within the vehicle cockpit, such that in case of anemergency maneuver, sudden acceleration, or crash, it does not fly aboutthe cockpit causing injury or burn hazards to passengers nor damagingother components of the vehicle. The present invention has split loopsaffixed to the outside of the cabinet which facilitate securing themicrowave oven in a seat with the seatbelt much as a child's safety seatwould. In the event of a collision the microwave oven described hereshuts down. It also has the usual safety features such as doorinterlocks and over-temperature sensors found in virtually all consumermicrowave ovens. Conventional mounting points are provided forsituations in which the device may be bolted down.

[0011] The invention described herein also places the intake and exhaustfor the cooling air required by the magnetron on the top surface suchthat the airflow is not impeded as it would be if mounted on a seat withdownward or side facing intakes and exhausts. The keypad is also mountedon the top surface for easy access.

[0012] The invention described herein also has an upward opening doorallowing access to the oven cavity. The cavity has a radio-transparent,removable, easily cleaned, plastic liner made of heat resistant plasticwhich contains any spills which may occur. These two features helpinsure that even if food somehow should spill within the oven, that itwill not leak out into the vehicle cabin. The door is retained shut by alocking mechanism when the oven is in operation and may stay in thatstate until an unlock button is pushed on the unit's keypad.

[0013] Since the vehicle may be in motion while the invention is in use,means must be provided of fixing the food container in place so that itdoes not “bounce around” and spill its contents nor damage the cavitywalls. In the preferred embodiment, a detented stud is centrally affixedto the center of the carousel. There are mating cavities molded into“microwave safe” plastic heating containers with locking lids andappropriate vents. The food is placed into the container, the vented lidis affixed with a latching lip or similar arrangement, and the cavity,typically in the center of the container is pressed down onto thedetented stud which retains it in place. Food portions in disposableheating containers, such as “Chef Boyardee® Lasagna, Microwave Meals,(10.5 oz. size)” can be manufactured with the appropriate mating cavitymolded in.

[0014] Alternatively an inverted pyramidal well is molded into aradio-transparent, heat resistant plastic support sheet. Food inappropriate containers is placed down into the well until contact ismade with the walls of the well. Alternatively a curved non-metallicspring-loaded radio-transparent wall could be used as retention device.

[0015] A carrying handle is molded into the top surface to facilitatehandling of the mobile microwave oven. A DC input cable terminated in a“cigarette lighter” plug or other suitable connector of sufficientlength and sufficient gauge is provided so that the invention may beinstalled in the back seat of long vehicles while being plugged into the“cigarette lighter” or “accessory socket” which is usually proximal tothe vehicle's front seat.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1: Mobile Microwave Oven

[0017]FIG. 1A: Keypad for Mobile Microwave Oven

[0018]FIG. 2: Mobile Microwave Oven Interior

[0019]FIG. 3: Mobile Microwave Oven Door, Door Locking Solenoid, andInterlock

[0020]FIG. 4: Mobile Microwave Oven System Diagram

[0021]FIG. 5: Inverted Pyramidal Food Retainer and Cavity Liner

[0022]FIG. 5A: Food Container Retention Stud

[0023]FIG. 6: View of Mobile Microwave Oven in Seat Retained by Seatbelt

[0024]FIG. 7: Side View of Mobile Microwave Oven in Seat Retained bySeatbelt

[0025]FIG. 8: Mobile Microwave Oven Operational Flowchart

DETAILED DESCRIPTION OF DRAWINGS DESCRIPTION OF SYSTEM

[0026] The LOW-POWER MOBILE MICROWAVE OVEN is typically placed on apassenger seat. On its top surface are the CONTROL KEYPAD AND DISPLAY(60), the magnetron COOLING AIR INTAKE (80) and OUTLET (110), and theupward opening microwave CAVITY DOOR (160) affixed by HINGE (150). TheHINGE (150) can be positioned on any of the four sides of the MICROWAVECAVITY (120) opening in The door seals the cavity so as to contain allmicrowave energy by means of conductive elastomeric GASKET (210) andconventional choke seal design.

[0027] The mobile microwave oven CABINET (200) is secured in place onthe seat by running the seatbelt for that seat through the SPLIT LOOPS(190) attached to the CABINET (200). The waist portion of the seatbeltis tightened to secure the CABINET (200) in place. The SPLIT LOOPS (190)are angled down from the vertical plane toward the seatback so as tofacilitate force components acting on the CABINET (200) down toward theseat cushion and backward toward the seatback without kinking ornarrowing of the belt where it passes through the SPLIT LOOPS (190).This method is similar to that used to secure infant and child safetyseats in vehicles. Alternatively, angle brackets and screws suitablyattached to the CABINET (200) can be used to effect a permanentmounting.

[0028] The “cigarette lighter” or “accessory power socket” PLUG (10) isinserted into the vehicle's “CIGARETTE LIGHTER” or “ACCESSORY” socket. Atwo-conductor insulated POWER CABLE (15) of at least #8 gauge attachedin series with the plug (10) brings power into the microwave oven'scabinet (200). This positive lead of this nominal 12 VDC power passesthrough the current sensing shunt (20) and is then bussed to the voltageregulator (30), the input of the switching power supply (40), and theinput of the Input voltage sensor comprised of A/D converter (70). It isalso connected to the DC fan motor control switch (95) and the doorlocking solenoid switch (185), and the oven cavity lamp switch (125).The 12 VDC rating in a vehicle is nominal and is usually closer to 14VDC when the vehicle engine is above idle speed

[0029] The voltage regulator (30) is a simple series pass regulatorwhich outputs +5 VDC at sufficient current to operate the systemcontroller (50), the keypad/display (60) and associated components. Itsdevices have voltage ratings which are suitable for use in theautomotive electrical environment and will survive the transients knownto exist in this environment.

[0030] The switching power supply (40) is an inverter type switchingpower supply with a 12 VDC nominal input. It outputs the magnetronfilament power, typically about 3 VDC at several amperes as well as theB- voltage, typically about 2-4 kV and in this application about 75-100mA at 2 kV. The exact voltages depend on the specific characteristics ofthe magnetron (100). The magnetron anode is typically grounded to themicrowave oven case (200) and the cathode to anode potential necessaryfor operation is developed by depressing the isolated or “floating”cathode filament below ground potential with the negative voltage. Themagnetic field of the magnetron is generated by permanent magnetsintegral with its housing. While magnetrons operating at the typical2450 MHz frequency have been used in a prototype of this invention,other frequencies might be employed to optimize energy transfer into orenergy modes in the microwave oven cavity. The switching power supply(40) utilizes inductive transformers whose wire windings, insulation andother mechanical construction produce satisfactory insulation andisolation so that the magnetron (100) filament can be safely floated,and so that the high voltage output is not compromised. The 3 VAC outputis electrically floating and connected with wires with insulation ofadequate voltage rating.

[0031] The switching power supply operates at a frequency much higherthan that of a typical AC line (60 Hz) and therefore requires lessenergy storage on the output. Consequently the power supply output canbe keyed on and off very rapidly by means of the PS (Power Supply)ENABLE SIGNAL from the System Controller (50). In the preferredembodiment, the Power supply is driven by a PS (Power Supply) CLOCKgenerated in firmware by the SYSTEM CONTROLLER (50), alternatively aseparate clock signal generator could be used.

[0032] The SYSTEM CONTROLLER (50) is a microprocessor with associatedRAM and ROM adequate for operation. Power is taken from VOLTAGEREGULATOR (30) which also serves to isolate and decouple the SYSTEMCONTROLLER (50) and related components from transients that occur invehicle power systems. Inputs to the SYSTEM CONTROLLER (50) are InputVoltage Reading; Vr output by A/D CONVERTER (70), Input Current Reading,Ir, developed by CURRENT SHUNT (20) and A/D CONVERTER (75), theACCELEROM signal output by ACCELEROMETER (300), LOGIC CLOCK output byCLOCK GENERATOR (350), INTERLOCK SIGNALS from the DOOR CLOSED INTERLOCKSWITCH (180) and the OVER TEMPERATURE SENSOR (175) and KEYSTROKE DATAgenerated by CONTROL KEYPAD AND DISPLAY (60).

[0033] Since this is a relatively low-power microwave oven, heatingtimes are longer than those of conventional, more powerful microwaveovens typically found in kitchens. The invention described here haspower input to the cavity of approximately one fourth of the power foundin typical kitchen microwave ovens. Most people who use a microwave ovenare familiar with “standard” heating times. These familiar times must bemultiplied by a factor of approximately four in order to be correct forthe lower power level in this invention. If a “standard” heating time isentered via the CONTROL KEYPAD AND DISPLAY (60), the SYSTEM CONTROLLER(50) multiplies the time by four in order to warm the food to the propertemperature. Since longer intervals allow more cooling by radiation andconvection, a manufacturer might adjust the time further with a lookuptable or algorithm based on empirical results. A surface pyrometer orother temperature sensor could also signal that desired temperature hasbeen reached.

[0034] The CONTROL KEYPAD AND DISPLAY (60) generates unique digitalsignals in a format suitable for input to the SYSTEM CONTROLLER (50),whenever a key is pressed. This subsystem also contains display driverswhich cause symbols and digits to appear in the multi-segmentmulti-character alphanumeric display when appropriate data is receivedfrom the SYSTEM CONTROLLER (50).

DESCRIPTION OF OPERATION

[0035] The Low-power microwave Oven is placed in a seat in a vehicle.The waist belt portion of the seatbelt corresponding to that seat ispassed through the SPLIT LOOPS (190). The waist belt is tightened downto secure the CABINET (200) in the seat.

[0036] The PLUG (10) is inserted into the “cigarette lighter” or“accessory power” socket of the vehicle in order to obtain 12 VDC power.The VOLTAGE REGULATOR (30) regulates the 12 VDC input to +5 VDC requiredby the SYSTEM CONTROLLER (50) and the CLOCK GENERATOR (350).

[0037] The DOOR (160) of the MICROWAVE CAVITY (120) swings open on HINGE(150). The user places the food or other substance to be heated in a“microwave safe”, radio-transparent heating container with a lockingvented lid. If the heating container has a mating recess molded into thebottom, the container can be “popped” onto the DETENTED RETAINER STUD(140). If there is no retaining component on the heating container thePLASTIC LINER WITH INVERTED PYRAMIDAL WELL (145), is used. Thiscomponent (145) made of radio-transparent, heat-resistant plastic, issimply placed in the microwave oven CAVITY (120) in place of the PLASTICLINER (130). The food container described above is placed as far downinto the well as it will go, thus retaining it in most situations. TheDOOR (160) is closed, the SPRING LATCHING PIN (175) is captured by theretaining RETAINING SPRING CATCH (170) and pressing on DOOR INTERLOCKSWITCH (180) which closes, sending a logic level signal to the SYSTEMCONTROLLER (50).

[0038] The user enters the length of time the food is to be heated. Ifthe user presses “STANDARD” on the “CONTROL KEYPAD AND DISPLAY(60)”, theSYSTEM CONTROLLER (50) multiplies by a factor which compensates for thelow-power feature of this microwave oven. Typically this factor will bein the range of 2-6. If the user does not press the “STANDARD” key, thetime entered not multiplied and represents the exact heating time.

[0039] The user presses the “START” key on the CONTROL KEYPAD ANDDISPLAY (60). The SYSTEM CONTROLLER (50) looks at all input signalsafter receiving the “START” signal. The following signals must bepresent:

[0040] INTERLOCKS: DOOR INTERLOCK SWITCH (180) actuated by closure ofcavity DOOR (160) in series with OVER TEMPERATURE SENSOR (175) Pulls“INTERLOCKS” line to ground.

[0041] Vr: Voltage reading from A/D CONVERTER (70) must be above minimumAcceptable battery voltage, nominally 11.5 volts.

[0042] Ir: Current reading from A/D CONVERTER (75) must be below maximumcurrent rating of power socket in vehicle. Set by manufacturer as afunction of intended usage, nominally 15 amperes in a small car, as highas 30 amperes in some larger trucks.

[0043] If not all conditions are satisfied, a “BEEP” command is sent tothe piezoelectric annunciator to inform the user. If all conditions aresatisfied the SYSTEM CONTROLLER (50) begins the heating of the food inits heating container. This is commanded by outputting the followingsignals and causing the following actions:

[0044] PS ENABLE: This signal enables SWITCHING POWER SUPPLY (40)operation.

[0045] PS CLOCK: This signal drives the power switching circuits in theSWITCHING POWER SUPPLY (40) thus supplying filament voltage 3 VAC aswell as negative high voltage B- to the cathode (filament).

[0046] MAG FAN ON: This signal drives the switch transistor (92) whichcauses the DC FAN MOTOR to turn the attached FAN BLADES (85). This drawsair in through top-mounted cooling air intake and circulates it throughthe attached PLENUM (82) past the DC FAN MOTOR (90) through theMAGNETRON ANODE THERMAL RADIATOR (105) and exhausts it via PLENUM (112)through top-mounted COOLING AIR OUTLET (110).

[0047] LOCKDOOR: This signal actuates the DOOR LOCK SOLENOID (390) bydriving the switch transistor (395).

[0048] After the inputted time interval has elapsed the SYSTEMCONTROLLER (50) ceases outputting all the signals necessary for theheating to occur and the DOOR (160) is unlocked. If any of the signalsrequired by the SYSTEM CONTROLLER (50) are lost, (50) ceases outputtingthe signals required for heating to occur.

[0049] The preferred embodiment described demonstrates the advantages ofthe invention. Variations on the embodiment described can be made toaccommodate different installation configurations. For example, theDETENTED RETAINER STUD (140) could be moved to one of the four otherstationary CAVITY (120) walls, enabling a conventional “front-opening”microwave oven with a vertical HINGE (150).

What is claimed is:
 1. A low-power microwave oven capable of operatingfrom the DC power normally available in passenger vehicles and boatsthrough the “cigarette lighter” or “accessory power” socket and havingmeans of using a seatbelt to secure the microwave oven in a seat of avehicle, comprising; A compact microwave oven cabinet enclosing a cavityor heating chamber, whose walls are constructed of a radio reflectingmaterial such as metal sheet, having a similarly constructed doorallowing access to the cavity, a source of microwave energy, amagnetron, suitable for operation at the power levels described,receiving power at appropriate voltages from a switching power supplyderiving its power from the vehicle “cigarette lighter” or “accessorypower” socket.
 2. Means for the microwave oven described in claim 1 withits control keypad and display, and cavity door, on the same top surfacesuch that they may be easily accessed while the microwave is secured ina seat of a vehicle and so that food may be easily placed into, andremoved from, the microwave oven cavity. Cooling air intake and outleton the same top surface so they are not blocked, occluded, ,nor airflowthrough them impeded, by proximity to the seat components or otherstructures.
 3. The microwave oven described in claim 2 with a DC motorhaving affixed to its shaft a set of fan blades and positioned so as tointake air from a top surface mounted vent and plenum, propel the airthrough the magnetron anode cooling structure and then through anadditional plenum out another top surface mounted vent.
 4. The microwaveoven described in claim 3 with a voltage regulator always on when thedevice is connected to the vehicle power source, providing power atappropriate voltage for the various logic and control circuits.
 5. Themicrowave oven described in claim 4 with a solenoid operated lockingmechanism to prevent the cavity door from springing open while thevehicle is in motion and thus releasing microwave energy into thevehicle.
 6. The microwave oven in claim 5 with a means, a detented stud,of retaining molded “microwave safe” food containers with locking lidsand appropriate vents in place while a vehicle is in motion by means ofa mating cavity or other retaining structure molded in to the bottom ofthe food container.
 7. The microwave oven in claim 6 with a removablemolded, radio-transparent, heat-resistant, dishwasher-safe plastic linerconstructed to fit closely into the microwave oven cavity and coveringthe bottom except for a clearance hole for the detented stud andextending most of the way up the sides of the cavity, but open at thetop.
 8. The microwave oven in claim 7 with a different removable molded,radio-transparent, heat-resistant, dishwasher-safe plastic linerconstructed to fit closely into the microwave oven cavity and having aninverted pyramidal well into which food heating containers may be placedso as to be constrained from movement while the vehicle is in motion. 9.The microwave oven in claim 8 with a digital system controllerconsisting of a microprocessor, adequate RAM and ROM and input buffersand output drivers which monitors acceleration signals from anaccelerometer or similar spatial displacement measuring devices as wellas cavity door and over temperature interlocks and other sensors relatedto safety concerns, and which causes immediate system shutdown in theevent of a hazardous or fault condition.
 10. The microwave oven in claim9 with an algorithm to multiply a “standard” heating time for a typicalfull-size kitchen microwave, and input to the system controller inputvia the control keypad, by a factor properly compensating for the lowerpower output and consequent longer heating time required in thislower-power microwave oven.
 11. The microwave oven in claim 10 with a DCmotor driving a cooling fan for a magnetron supplied with power directlyfrom the vehicle via a transistor switch and whose intake and exhaustairflow is contained within plenums vented to the outside of thecabinet.
 12. The microwave oven in claim 11 with a means of monitoringinput voltage and input current to the system and causing systemshutdown in the event that the vehicle battery voltage drops below anacceptable level or if the current being drawn rises near a level whichwill cause the vehicle power outlet fuse to blow or which is otherwiseunacceptable.
 13. The microwave oven in claim 12 with a carrying handlemolded into the top surface or externally affixed thereto so as to notinterfere with any other required functions.
 14. The microwave oven inclaim 13 with an external cabinet or housing constructed of atransparent or translucent material which allows viewing of the internalcomponents and construction.
 15. A low-power mobile microwave oven foruse in a vehicle or boat comprising; a cabinet enclosing a cavity orheating chamber, whose walls are constructed of a radio reflectingmaterial such as metal sheet, a magnetron for providing microwave energyto the heating chamber, a switching power supply that supplies energy tothe magnetron, means for supplying power to the switching power supply,and wherein the cabinet defines a top surface, wherein the controls forthe oven, a control keypad and display, the cooling air inlets andoutlets and a door that provides access to the heating chamber or cavityare all provided on the top surface.
 16. A low-power mobile microwaveoven for use in a vehicle or boat comprising; a cabinet enclosing acavity or heating chamber, whose walls are constructed of radioreflecting material such as metal sheet, and wherein the cabinetcontains a door that provides access to the heating chamber, controlsfor the oven, a control keypad and display, and air inlet and outlets, amagnetron for providing microwave energy to the heating chamber orcavity, a switching power supply that supplies energy to the magnetron,a plug and cable from the “cigarette lighter” or “accessory power”socket or similar connector for supplying power to the switching powersupply.
 17. A low-power mobile microwave oven for use in a vehicle suchas a car, a boat, or an aircraft, wherein the vehicle contains seatbelts, comprising; a cabinet enclosing a cavity or heating chamber,whose walls are constructed of a 'radio reflecting material such asmetal sheet, and wherein the cabinet contains a door that providesaccess to the heating chamber, controls for the oven, a keypad anddisplay, and air inlets and outlets, a magnetron for providing microwaveenergy to the heating chamber, a switching power supply that suppliesenergy to the magnetron, means for supplying power to the switchingpower supply, and means for securing the oven to a seat by the seatbelts.
 18. A low-power mobile microwave oven for use in a vehicle orboat comprising; a cabinet enclosing a cavity or heating chamber, whosewalls are constructed of radio reflecting material such as metal sheet,and wherein the cabinet contains a door that provides access to theheating chamber, controls for the oven, a control keypad and display,and air inlets and outlets, a magnetron for providing microwave energyto the heating chamber or cavity, a switching power supply that suppliesenergy to the magnetron, and means for supplying power to the switchingpower supply wherein the total power consumption is less than 300 Watts.